Fuel cell stack with internal fuel manifold configuration

ABSTRACT

A fuel cell stack includes a plurality of fuel cells, and a plurality of fuel delivery ports. Each of the plurality of fuel delivery ports is positioned on or in the fuel cell stack to provide fuel to a portion of the plurality fuel cells in each stack.

This application claims benefit of priority of U.S. ProvisionalApplication Ser. No. 60/660,515, filed on Mar. 10, 2005, which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention is generally directed to fuel cells and morespecifically to fuel cell stack configuration.

Fuel cells are electrochemical devices which can convert energy storedin fuels to electrical energy with high efficiencies. High temperaturefuel cells include solid oxide and molten carbonate fuel cells. Thesefuel cells may operate using hydrogen and/or hydrocarbon fuels. Thereare classes of fuel cells, such as the solid oxide reversible fuelcells, that also allow reversed operation.

In a high temperature fuel cell system such as a solid oxide fuel cell(SOFC) system, an oxidizing flow is passed through the cathode side ofthe fuel cell while a fuel flow is passed through the anode side of thefuel cell. The oxidizing flow is typically air, while the fuel flow istypically a hydrogen-rich gas created by reforming a hydrocarbon fuelsource. The fuel cell, operating at a typical temperature between 750°C. and 950° C., enables the transport of negatively charged oxygen ionsfrom the cathode flow stream to the anode flow stream, where the ioncombines with either free hydrogen or hydrogen in a hydrocarbon moleculeto form water vapor and/or with carbon monoxide to form carbon dioxide.The excess electrons from the negatively charged ion are routed back tothe cathode side of the fuel cell through an electrical circuitcompleted between anode and cathode, resulting in an electrical currentflow through the circuit.

Fuel cell stacks may be either internally or externally manifolded forfuel and air. In internally manifolded stacks, the fuel and air isdistributed to each cell using risers contained within the stack Inother words, the gas flows through riser openings or holes in thesupporting layer of each cell, such as the electrolyte layer, forexample. In externally manifolded stacks, the stack is open on the fueland air inlet and outlet sides, and the fuel and air are introduced andcollected independently of the stack hardware. For example, the inletand outlet fuel and air flow in separate channels between the stack andthe manifold housing in which the stack is located.

BRIEF SUMMARY OF THE INVENTION

The preferred aspects of present invention provide a fuel cell stack,comprising a plurality of fuel cells, and a plurality of fuel deliveryports. Each of the plurality of fuel delivery ports is positioned on orin the fuel cell stack to provide fuel to a portion of the pluralityfuel cells in each stack.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side cross sectional view of a stack of oneembodiment of the present invention.

FIG. 2 is a schematic side cross sectional view of a stack of anotherembodiment of the present invention.

FIG. 3 is a schematic three dimensional view of a fuel manifold shown inFIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventors realized a novel approach to fuel cell stacks thatare internally manifolded at least on the fuel side The fuel cellscontain small (i.e., narrow or small diameter) fuel riser openings, suchas openings having a cross sectional width of 0.5 inches or less, Thebenefits of a small internal fuel manifold include reduced material andfabrication cost, less failures in the electrolyte, larger availablecross section for air flow, and increased active area.

The present inventors also realized that in a stack with internalmanifolding on the fuel side having riser openings with a small crosssectional width, the pressure drop from the top to the bottom of thestack may be large which may limit stack height. In order to increasestack height, a plurality of fuel delivery ports may be positioned in oron the fuel cell stack to provide fuel to a portion of the fuel cells ineach stack. The fuel delivery ports may be placed at periodic intervalsup the stack feeding only a limited number of fuel cells. Thisconfiguration prevents or reduces large pressure differentials fromdeveloping that cause fuel flow non-uniformity. If desired, the fueldelivery ports may be connected to internal fuel manifolds (i.e., pipesor chambers having a plurality of openings for making connections)located between adjacent fuels cells of the stack.

FIG. 1 is a schematic illustration of a fuel cell stack 1 of a firstembodiment of the invention containing a plurality of fuel delivery orinlet ports 3. While two ports 3 are shown in FIG. 1 for clarity, itshould be understood that more than two ports 3, such as three to tenports, for example, may be provided. The fuel provided through the ports3 circulates through fuel inlet riser openings 5 into the fuel cells 7and then exits the fuel cells 7 through fuel outlet riser openings 9.The fuel exhaust is provided into fuel outlet ports 11 from the outletriser openings 9. Preferably, the stack 1 contains a plurality of fueloutlet ports 11, such as two or more such ports.

The fuel inlet riser openings 5 and the fuel outlet riser openings 9comprise openings or holes which extend through at least one layer ofthe fuel cells 7. For example, for electrolyte supported fuel cells, theopenings 5 and 9 extend at least through the electrolyte. For electrodesupported fuel cells, such as anode or cathode supported fuel cells, theopenings 5 and 9 extend at least through the supporting electrode. Ofcourse the openings 5, 9 may extend through two or more layers of thefuel cells as well as through the interconnects/gas separators which arelocated between adjacent fuel cells. Preferably, the fuel riser inlet 5and outlet 9 openings have a cross sectional width of about 0.5 inchesor less, such as 0.15 to 0.5 inches, for example 0.25 to 0.4 inches. Forexample, the openings 5, 9 may comprise openings having a round crosssectional shape and having a diameter of 0.15 to 0.5 inches. However,the openings 5, 9 may have other cross sectional shapes, such aspolygonal, oval, or other suitable shapes.

Each of the plurality of fuel delivery ports 3 is positioned in the fuelcell stack 1 to provide fuel to a portion of the plurality fuel cells 7in or on each stack. In other words, the fuel delivery ports 3 may belocated “on” the stack 1 by being connected to fuel manifolds which arelocated between the fuel cells or the fuel delivery ports 3 may belocated “in” the stack 1 by being directly connected to fuel inlet riseropenings 5 in the stack 5. The fuel from each fuel delivery port 3 ispreferably provided to less than all fuel cells 7 in the stack 1.However, it should be noted that the term “provide fuel to a portion ofthe plurality fuel cells” does not necessarily exclude allowing the fuelfrom a particular port 3 from circulating through the entire stack 1,with the other port(s) 3 providing supplemental fuel in other portionsof the stack 1.

As noted above, the stack I is internally manifolded for fuel. Thus,fuel is distributed to each fuel cell 7 using riser openings 5, 9contained within the stack 1. The stack 1 may be internally orexternally manifolded for oxidizer, such as air. Preferably, the stack 1is externally manifolded for oxidizer, Thus, the stack 1 is open on theair inlet and outlet sides, and the air is introduced and collectedindependently of the stack hardware.

The stack 1 may comprise any suitable shape. Preferably, the stack 1comprises a planar type stack containing plate shaped (i.e., planar)fuel cells 7, The stack may be positioned in any suitable direction fromvertical to horizontal. Preferably, the stack is positioned vertically,with each fuel cell being located over the adjacent fuel cell below. Thefuel delivery ports 3 and the fuel outlet ports 11 may be positionedperiodically up the stack 1, as shown in FIG. 1.

Preferably, the fuel cells 7 comprise solid oxide fuel cells. However,the fuel cells may comprise other fuel cell types, such as moltencarbonate fuel cells, for example. Any suitable fuel may be providedinto the fuel cells. For example, hydrogen and/or hydrocarbon fuel, suchas methane or natural gas, may be provided into the fuel cells.

FIG. 2 shows a side cross sectional view of a fuel cell stack 101according to a second embodiment of the invention. In the stack 101, atleast one fuel delivery port 103 is connected to a fuel manifold 113located between adjacent plate shaped fuel cells 107. In one example,the stack 103 contains a plurality of fuel delivery ports 103 and aplurality of fuel outlet ports 111 as described with respect to thefirst embodiment above. The stack 103 also contains a plurality of fuelmanifolds 113, such that each of the plurality of fuel delivery ports103 is connected to a respective one of a plurality of fuel manifolds113. The stack 103 comprises a complete and independent electricalentity.

In another example, the stack 103 contains only one fuel manifold 113which is located between adjacent plate shaped fuel cells 107. In otherwords, the fuel manifold 113 is located between the fuel cells 107 inthe stack rather than at the edge of the stack between the last (i.e.,edge) fuel cell in the stack and an end plate of the stack.

The fuel manifold 113 may have any suitable configuration, such as apipe or chamber configuration. For example, as shown in FIG. 3, the fuelmanifold may comprise a chamber configured as a plate shaped box. Thebox may have any suitable cross sectional shape, preferably a shapewhich matches the cross sectional shape of the fuel cells. For example,the cross sectional shape of the fuel manifold may comprise a polygon,such as a triangle, rectangle, square, etc., a circle, an oval or othersuitable shape. The plate shaped box 113 contains major surfaces 115 orfaces and narrower edge surfaces 116.

The box 113 contains at least one fuel delivery opening 117 in fluidcommunication with fuel cell fuel inlet riser openings 105 and at leastone fuel outlet opening 119 in fluid communication with fuel cell fueloutlet riser openings 109. For example, as shown in FIGS. 2 and 3, afirst fuel delivery opening 117A and a first fuel outlet opening 119Aare located in a first major plate face 115A of the plate shaped box,and a second fuel delivery opening 117B and a second fuel outlet opening119B are located in a second major plate face 115B of the plate shapedbox 113. The fuel manifold 113 also contains a fuel delivery port 103comprising a fuel inlet conduit adapted to provide a fuel inlet streaminto the fuel manifold 113. The fuel manifold 113 also contains a fueloutlet port 111 comprising a fuel outlet conduit adapted to remove aspent fuel outlet or exhaust stream from the fuel manifold 113.Preferably, the fuel inlet and outlet conduits 103, 111 are locatednon-parallel with the fuel inlet 105 and outlet 109 riser openings. Forexample, as shown in FIGS. 2 and 3, the fuel inlet and outlet conduits103, 111 are located perpendicular to the fuel inlet 105 and outlet 109riser openings (i.e., the fuel inlet and outlet conduits 103, 111 arelocated perpendicular to the direction in which fuel inlet 105 andoutlet 109 riser openings extend).

As shown in FIG. 2, the fuel manifold 113 introduces fresh fuel fromfuel inlet port 103 into the fuel inlet riser openings 105 through fueldelivery openings 117A and 117B. The fuel flows from the fuel inletriser openings 105 through the fuel cells 107 (i.e., through fuel flowchannels between the fuel (anode) electrodes and the gasseparator/interconnect plates) and into the fuel outlet riser openings109. The spent or exhausted fuel (i.e., fuel exhaust) is provided fromthe fuel outlet riser openings 109 into the fuel outlet openings 119Aand 119B of the fuel manifold. The exhausted fuel is then removed fromthe stack 101 via the fuel outlet port 111. In the vertically positionedstack 101, the fuel flows up and down to and from the manifold 113through openings 105 and 109. However, if the stack 101 is positionedhorizontally, then the fuel would flow in horizontal planes throughopenings 105, 109,

FIG. 2 also shows the oxidizer (i.e., air) flow in the fuel cell stack101 that has an external manifolding configuration on the oxidizer side.The oxidizer (i.e., air) is provided from one side of the stack 103,travels through the fuel cells 107 (i.e., between the oxidizer (cathode)electrodes and gas separator/interconnect plates) and exits on theopposite side of the stack 103. In solid oxide fuel cells, a portion ofthe oxidizer (i.e., oxygen present in air) is transported through thefuel cell electrolyte in the form of oxygen ions and reacts with thefuel to generate the fuel exhaust, such as water. FIG. 2 shows a flowconfiguration where fuel and air flow in parallel but oppositedirections along the fuel cells 107. However, fuel and air may flow inparallel and same direction, or in perpendicular directions if desired.Furthermore, as noted above, the stack 10 may instead have an internalmanifolding configuration on the air side.

The foregoing description of the invention has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andmodifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention. Thedescription was chosen in order to explain the principles of theinvention and its practical application It is intended that the scope ofthe invention be defined by the claims appended hereto, and theirequivalents.

1. A fuel cell stack located within a manifold housing, the fuel cellstack comprising: a plurality of plate shaped fuel cells which areinternally manifolded on a fuel side and externally manifolded on anoxidizer side such that oxidizer is provided from a first side of thefuel cell stack for each of the plurality of plate shaped fuel cellsthrough a respective inlet in the first side of the fuel cell stack,travels between a cathode electrode of each of the plurality of plateshaped fuel cells and an adjacent interconnect plate, and exits througha respective outlet on a second side of the stack, wherein therespective inlets and outlets are exposed to, and communicate with, theinside of the manifold housing; and at least one fuel manifold locatedbetween adjacent fuel cells; wherein the at least one manifoldcomprises: a plate shaped box comprising at least one fuel deliveryopening in fluid communication with fuel cell fuel inlet riser openingsand at least one fuel outlet opening in fluid communication with fuelcell fuel outlet riser openings; a fuel delivery port comprising a fuelinlet conduit adapted to provide a fuel inlet stream into the fuelmanifold, and a fuel outlet port comprising a fuel outlet conduitadapted to remove a fuel outlet stream from the fuel manifold; andwherein the plate shaped box comprises a separate component from thefuel cells.
 2. The stack of claim 1, wherein the fuel inlet and outletriser openings are positioned substantially perpendicularly to the fuelinlet and the fuel outlet conduits.
 3. The stack of claim 2, wherein:the at least one fuel manifold comprises a first fuel delivery openingand a first fuel outlet opening located in a first major plate face ofthe plate shaped box, and a second fuel delivery opening and a secondfuel outlet opening located in a second major plate face of the plateshaped box; and the fuel inlet conduit and the fuel outlet conduit areconnected to at least one edge of the plate shaped box.
 4. The stack ofclaim 1, further comprising fuel inlet riser openings in the pluralityof fuel cells having a cross sectional width of 0.15 to 0.5 inches. 5.The stack of claim 1, further comprising a plurality of fuel deliveryports, wherein each of the plurality of fuel delivery ports is connectedto a respective one of a plurality of manifolds to provide fuel to aportion of the plurality fuel cells in each stack.
 6. The stack of claim1, wherein the plurality of plate shaped fuel cells are stacked in avertical direction.
 7. The stack of claim 6, wherein the plate shapedbox comprises: a top wall, a bottom wall, two opposite end walls, andtwo opposite side walls, said end walls and said side walls extendingupwardly from the bottom wall to the top wall, wherein said side wallsand end walls comprise edge surfaces, and wherein said top and bottomwalls comprise first and second major plate surfaces of the plate shapedbox.
 8. A fuel cell stack located within a manifold housing, the fuelcell stack comprising: a plurality of plate shaped fuel cells which areinternally manifolded on a fuel side and externally manifolded on anoxidizer side such that oxidizer is provided from a first side of thefuel cell stack for each of the plurality of plate shaped fuel cellsthrough a respective inlet in the first side of the fuel cell stack,travels between a cathode electrode of each of the plurality of plateshaped fuel cells and an adjacent interconnect plate, and exits througha respective outlet on a second side of the stack, wherein therespective inlets and outlets are exposed to, and communicate with, theinside of the manifold housing; and at least one fuel manifold locatedbetween adjacent fuel cells; wherein the at least one manifoldcomprises: a plate shaped box comprising at least one fuel deliveryopening in fluid communication with fuel cell fuel inlet riser openingsand at least one fuel outlet opening in fluid communication with fuelcell fuel outlet riser openings; a fuel delivery port comprising a fuelinlet conduit adapted to provide a fuel inlet stream into the fuelmanifold, and a fuel outlet port comprising a fuel outlet conduitadapted to remove a fuel outlet stream from the fuel manifold; whereinthe plate shaped box comprises a top wall, a bottom wall, two oppositeend walls, and two opposite side walls, said end walls and said sidewalls extending upwardly from the bottom wall to the top wall, whereinsaid side walls and end walls comprise edge surfaces, wherein said topand bottom walls comprise first and second major plate surfaces of theplate shaped box, and wherein at least one of the top and the bottomwalls of the plate shaped box are located adjacent to the plurality ofplate shaped fuel cells.
 9. The stack of claim 8, wherein the fuel inletand outlet riser openings are positioned substantially perpendicularlyto the fuel inlet and the fuel outlet conduits.
 10. The stack of claim9, wherein: the at least one fuel manifold comprises a first fueldelivery opening and a first fuel outlet opening located in the firstmajor plate surface of the plate shaped box, and a second fuel deliveryopening and a second fuel outlet opening located in the second majorplate surface of the plate shaped box; and the fuel inlet conduit andthe fuel outlet conduit are connected to at least one edge surface ofthe plate shaped box.
 11. The stack of claim 8, further comprising fuelinlet riser openings in the plurality of fuel cells having a crosssectional width of 0.15 to 0.5 inches.
 12. The stack of claim 8, furthercomprising a plurality of fuel delivery ports, wherein each of theplurality of fuel delivery ports is connected to a respective one of aplurality of manifolds to provide fuel to a portion of the pluralityfuel cells in each stack.
 13. The stack of claim 8, wherein theplurality of plate shaped fuel cells are stacked in a verticaldirection.
 14. The stack of claim 8, wherein the plate shaped boxcomprises a separate component from the fuel cells.